As indicated in U.S. Pat. No. 4,078,286, in a typical process for electrophotographic duplication, a light image of an original document to be copied is recorded in the form of a latent electrostatic image upon a photosensitive member, and the latent image is subsequently rendered visible by the application of electroscopic particles, which are commonly referred to as toner. The physical toner image is then in a loose powdered form and it can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support, which may be the photosensitive member itself or another support such as a sheet of plain paper. The present invention relates to the fusing of the toner image upon a support.
It should be understood that for the purposes of the present invention, which relates to the fusing of the toner image upon a support, the latent electrostatic image may be formed by means other than by the exposure of an electrostatically charged photosensitive member to a light image of an original document. For example, the latent electrostatic image may be generated from information electronically stored or generated, and the digital information may be converted to alphanumeric images by image generation electronics and optics. However, such image generation electronic devices and optic devices form no part of the present invention.
In order to fuse electroscopic toner material onto a support surface permanently by heat, it is usually necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to be firmly bonded to the support.
The use of thermal energy for fixing toner images onto a support member is well known. Several approaches to thermal fusing of electroscopic toner images have been described in the prior art. These methods include providing the application of heat and pressure substantially concurrently by various means: a roll pair maintained in pressure contact; a flat or curved plate member in pressure contact with a roll; a belt member in pressure contact with a roll; and the like. Heat may be applied by heating one or both of the rolls, plate members or belt members. The fusing of the toner particles takes place when the proper combination of heat, pressure and contact time are provided. In these contact fusing processes, it is important to insure that substantially no offset of the toner particles from the support to the fuser member takes place. It is known in the prior art to prevent offset by imparting release properties to the fuser member, or the pressure member by covering such members with a surface layer of a release material such as polytetrafluoroethylene, silicone rubber, or the like. A suitable offset preventing liquid may be used on the fuser member to minimize or avoid offsetting. Silicone oils are widely used as the offset preventing or release agent. Representative prior art disclosing such contact fusing include U.S. Pat. Nos. 4,078,286; 4,064,313; 3,809,854; 3,848,305; and 3,795,033. While such prior art contact fusing systems have been effective in providing the fusing of many copies in relatively large and fast copying and duplicating machines, in which the use of standby heating elements to maintain the machine at or near its operating temperature can be justified, there is a continuing need for an instant-on fuser which requires no standby power for maintaining the fuser apparatus at a temperature above the ambient. In addition, the prior art contact fusing systems are generally relatively expensive to construct, and thus they are primarily suited for use in relatively large and fast copying and duplicating machines.
It is also known in the art to fuse toner images by the use of a flash fusing process. An example of such a process is disclosed in U.S. Pat. No. 3,874,892. In such a flash fusing process, a flash lamp or other source of radiant energy is generally pulsed on for a very short period of time. The absorption of the radiant energy by the toner particles results in the fusing of the toner to the substrate. It can be appreciated that since the lamp is pulsed or flashed on for a short period of time, a large amount of power must be used to accomplish the fusing of the toner particles. Thus, one drawback of a flash fusing process is the relatively large and expensive power supply required. Another problem with flash fusing is image explosion whereby toner is evaporated with each flash and deposited on the wall of the fusing cavity. This necessitates the cleaning or replacing of the reflective lining in the flash fusing chamber.
Another method for fusing toner images to a substrate is radiant fusing. Radiant fusing differs from flash fusing, inter alia, in that in radiant fusing the radiant energy source, typically an infrared quartz lamp, is turned on during the entire fusing step, rather than pulsed on for a short period of time as in flash fusing. Examples of radiant fuser apparatus are shown in U.S. Pat. Nos. 3,898,424 and 3,953,709. Such prior art radiant fusers are generally made of relatively heavy metallic construction which requires the constant use of a heating element to maintain the apparatus at standby temperature.
In summary, while the prior art fusers have been effective in providing the fusing of copies in relatively large and fast copying and duplicating machines, in which the use of standby heating elements to maintain the machine at or near its operating temperature can be justified, there is a continuing need for an instant-on fuser which requires no standby power for maintaining the fuser apparatus at a temperature above the ambient.
Accordingly, it is an object of the invention to provide an improved fusing apparatus which can be instantly turned on and yet requires no standby power or heating element.
It is a further object of the present invention to provide an inexpensive fusing apparatus which is economical to operate.
These and other objects of the invention can be gathered from the following detailed disclosure.